1. The Biology of Aging and Cancer: A Brief Overview of Shared and Divergent Molecular Hallmarks
R. Aunan Jan 1, 2 ;C Cho William 3 ;S#cod#x000F8;reide Kjetil 1, 2, 4 ;
1 Gastrointestinal Translational Research Unit, Molecular Lab, Stavanger University Hospital, Stavanger, Norway ; 2 Department of Gastrointestinal Surgery, Stavanger University Hospital, Stavanger, Norway ; 3 Department of Clinical Oncology, Queen Elizabeth Hospital, Kowloon, Hong Kong ; 4 Department of Clinical Medicine, University of Bergen, Bergen, Norway ;
Figure 1. Lifelong interplay between stem cells in aging and cancer. A simplified model that views aging and cancer from the perspective of alterations within the stem and progenitor cell pool. Over the lifespan of an organism, long-lived cells such as stem cells accumulate DNA damage from a number of stresses including intracellular oxidants generated from normal metabolism. The default pathway for such damaged stem cells is to undergo growth arrest, apoptosis or senescence. As more and more stem cells withdraw from the proliferative pool, there is a decrease in the overall number andor functionality of both stem and progenitor cells. This decrease predisposes the organism to impaired tissue homeostasis and regenerative capacity and could contribute to aging and age-related pathologies. Presumably, some rare cells can escape from this normal default pathway by acquiring additional mutations that allow them to continue to proliferate even in the setting of damaged DNA. These proliferating but damaged cells might provide the seeds for future malignancies. In this scenario, both cancer and aging result primarily from accumulating damage to the stem and progenitor cell compartment. Mutations that allow stem cells to continue to proliferate in the setting of normal growth arrest signals such as DNA damage for example, loss of p16 INK4a or reactivation of telomerase would temporarily expand the stem cell pool and hence delay age-related pathologies. Over the long term, these mutations would also increase the likelihood of cancer. During normal aging, stem cells accumulate damage and subsequent stress-dependent changes, for example, de-repression of the CDKN2a p16 INK4a ARF locus or telomere shortening. This leads to the increasing abundance of senescent cells large hexagonal cells within differentiated tissues. Preneoplastic leasions, arising directly from stem cells or from more committed cells, undergo rapid proliferation small cells marked with asterisks. These pre-malignant tumor cells rapidly accumulate damage, in part owing to the presence of oncogenes, leading to a higher proportion of tumor cells becoming senescent cells marked as hexagons filled with white color. Tumor progression to full malignancy is favoured when tumor cells acquire mutations that impair the senescence program for example, mutations in Trp53 or CDKN2a . Illustration is modified and based upon Finkel T, Serrano M, Blasco MA. The common biology of cancer and aging. Nature Aug 16; : Copyright #cod#x000A9; 2007.
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